Effect of Reheating on Grain Size Evolution in High Strength Linepipe Steel

The effects of slab reheat temperature and soaking time are studied to characterize austenite grain growth, microstructure homogeneity and dissolution of precipitates in linepipe X80 grade steel. It is shown that the uniformity of austenite microstructure strongly depends on the slab reheat temperature and soaking time. With increasing reheat temperature an abnormal growth of individual grains is observed that stems from gradual dissolution of microalloy carbonitrides. As the result, individual grain boundaries become unpinned and mobile thus "nucleating" secondary recrystallization. The highest reheat temperature at which the dissolution kinetics of precipitates is still slow enough to prevent the onset of secondary recrystallization within long soaking times is 1160°C. The as reheated austenite microstructure and the character of austenite grain size distribution are inherited throughout the entire roughing rolling sequence and even further downstream to the finishing rolling entry. The effects of reheat soaking time on shear fracture area and impact toughness are also described.

Download Full-text

Development and Industrial Applying on Rolling Mill 5000 of the Model of Austenite Grain Size Evolution in Nb-Microalloyed Steels

Materials Science Forum ◽

10.4028/www.scientific.net/msf.879.312 ◽

2016 ◽

Vol 879 ◽

pp. 312-317

Author(s):

A.V. Chastukhin ◽

D.A. Ringinen ◽

S.V. Golovin ◽

L.I. Efron

Keyword(s):

Grain Size ◽

Rolling Mill ◽

Microalloyed Steels ◽

Compression Tests ◽

Austenite Grain Size ◽

Soaking Time ◽

Austenite Grain ◽

Size Evolution ◽

South Stream ◽

Rolled Plates

In this research evolution of austenite grain size in Nb-microalloyed steels X65÷X120 grades during slab reheating and roughing rolling was studied. A mathematical model has been development to obtain the target temperature and soaking time in furnace, which ensure a uniform austenite structure and maximum possible dissolution of the carbonitride particles prior to roughing rolling. The Hot Rolling Recrystallization Model (HRRM) has also development to predict the austenite microstructure evolution during roughing rolling. The model is based on empirical equations and organized following a tree-structure. A validation of the model has been carried out in the laboratory by multipass compression tests. The models jointly have been used to create new strategies of processing technology of rolled plates on rolling mill 5000 for the South Stream pipeline. The industrial application has confirmed a great benefit of the models in point of cold resistance of rolled plates.

Download Full-text

Grain Size Evolution and Mechanical Properties of Nb, V–Nb, and Ti–Nb Boron Type S1100QL Steels

Metals ◽

10.3390/met11030492 ◽

2021 ◽

Vol 11 (3) ◽

pp. 492

Author(s):

Jan Foder ◽

Jaka Burja ◽

Grega Klančnik

Keyword(s):

Mechanical Properties ◽

Heat Treatment ◽

Grain Size ◽

Hot Forging ◽

Size Control ◽

High Strength ◽

Fatigue Properties ◽

Titanium Addition ◽

Austenite Grain Size ◽

Size Evolution

Titanium additions are often used for boron factor and primary austenite grain size control in boron high- and ultra-high-strength alloys. Due to the risk of formation of coarse TiN during solidification the addition of titanium is limited in respect to nitrogen. The risk of coarse nitrides working as non-metallic inclusions formed in the last solidification front can degrade fatigue properties and weldability of the final product. In the presented study three microalloying systems with minor additions were tested, two without any titanium addition, to evaluate grain size evolution and mechanical properties with pre-defined as-cast, hot forging, hot rolling, and off-line heat-treatment strategy to meet demands for S1100QL steel. Microstructure evolution from hot-forged to final martensitic microstructure was observed, continuous cooling transformation diagrams of non-deformed austenite were constructed for off-line heat treatment, and the mechanical properties of Nb and V–Nb were compared to Ti–Nb microalloying system with a limited titanium addition. Using the parameters in the laboratory environment all three micro-alloying systems can provide needed mechanical properties, especially the Ti–Nb system can be successfully replaced with V–Nb having the highest response in tensile properties and still obtaining satisfying toughness of 27 J at –40 °C using Charpy V-notch samples.

Download Full-text

Overview of HSS Steel Grades Development and Study of Reheating Condition Effects on Austenite Grain Size Changes

Materials ◽

10.3390/ma14081988 ◽

2021 ◽

Vol 14 (8) ◽

pp. 1988

Author(s):

Tibor Kvackaj ◽

Jana Bidulská ◽

Róbert Bidulský

Keyword(s):

Mechanical Properties ◽

Grain Size ◽

High Strength Steel ◽

Single Phase ◽

Hsla Steel ◽

High Strength ◽

Strength Properties ◽

Austenite Grain Size ◽

Austenite Grain ◽

Steel Grades

This review paper concerns the development of the chemical compositions and controlled processes of rolling and cooling steels to increase their mechanical properties and reduce weight and production costs. The paper analyzes the basic differences among high-strength steel (HSS), advanced high-strength steel (AHSS) and ultra-high-strength steel (UHSS) depending on differences in their final microstructural components, chemical composition, alloying elements and strengthening contributions to determine strength and mechanical properties. HSS is characterized by a final single-phase structure with reduced perlite content, while AHSS has a final structure of two-phase to multiphase. UHSS is characterized by a single-phase or multiphase structure. The yield strength of the steels have the following value intervals: HSS, 180–550 MPa; AHSS, 260–900 MPa; UHSS, 600–960 MPa. In addition to strength properties, the ductility of these steel grades is also an important parameter. AHSS steel has the best ductility, followed by HSS and UHSS. Within the HSS steel group, high-strength low-alloy (HSLA) steel represents a special subgroup characterized by the use of microalloying elements for special strength and plastic properties. An important parameter determining the strength properties of these steels is the grain-size diameter of the final structure, which depends on the processing conditions of the previous austenitic structure. The influence of reheating temperatures (TReh) and the holding time at the reheating temperature (tReh) of C–Mn–Nb–V HSLA steel was investigated in detail. Mathematical equations describing changes in the diameter of austenite grain size (dγ), depending on reheating temperature and holding time, were derived by the authors. The coordinates of the point where normal grain growth turned abnormal was determined. These coordinates for testing steel are the reheating conditions TReh = 1060 °C, tReh = 1800 s at the diameter of austenite grain size dγ = 100 μm.

Download Full-text

The Influence of Initial Grain Size and Strain Sequence of Slab Hot Rolling on the Austenite Evolution of Peritectic Microalloyed Plate Steels

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1019.339 ◽

2014 ◽

Vol 1019 ◽

pp. 339-346 ◽

Cited By ~ 1

Author(s):

Rorisang Maubane ◽

Kevin Banks ◽

Waldo Stumpf ◽

Charles Siyasiya ◽

Alison Tuling

Keyword(s):

Grain Size ◽

Hot Rolling ◽

Plain Carbon Steel ◽

Microalloyed Steels ◽

Heating Rates ◽

Austenite Grain Size ◽

Soaking Time ◽

Austenite Grain ◽

Dynamic Recrystallisation ◽

Temperature Constant

The influence of the strain sequence during slab hot rolling (also known as “roughing”) on the evolution of austenite in plain carbon, C-Mn-V and C-Mn-Nb-Ti-V steels was investigated. Reheating and roughing simulations were conducted in a Bähr deformation dilatometer using a constant austenitising temperature, constant soaking time and various heating rates and roughing strain sequences. Stress analysis was used to quantify the austenite softening behaviour and the prior austenite grain size was measured from quenched specimens. The austenite grains of the plain carbon steel were coarser than those of both microalloyed steels, with the C-Mn-Nb-Ti-V grade being the finest due to effective pinning of the grain boundaries. Pass strains greater than 0.2 were sufficient for initiation of dynamic recrystallisation (DRX) for the C-Mn and C-Mn-V steels and led to uniform austenite microstructure with austenite grain sizes less than 40µm after the roughing stage.

Download Full-text

Investigation of the Austenite Grain Growth in HY-TUF Steel

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.299.482 ◽

2020 ◽

Vol 299 ◽

pp. 482-486

Author(s):

Mikhail V. Maisuradze ◽

Maksim A. Ryzhkov

Keyword(s):

Grain Size ◽

Grain Growth ◽

Heating Temperature ◽

High Strength ◽

Silicon Steel ◽

Austenite Grain Size ◽

Austenite Grain ◽

Austenite Grains ◽

Austenite Grain Growth ◽

Intensive Growth

The high strength silicon steel HY-TUF, applied for manufacturing of the heavy loaded aerospace and engineering parts, was investigated. The effect of the heating temperature in the range 900...1000 °C on the austenite grain size was studied. The steel under consideration had a significant scatter of the austenite grain size. The most intensive growth of the austenite grains was observed in the temperature range 975...1000 °C.

Download Full-text

New insights from crystallography into the effect of refining prior austenite grain size on transformation phenomenon and consequent mechanical properties of ultra-high strength low alloy steel

Materials Science and Engineering A ◽

10.1016/j.msea.2018.12.057 ◽

2019 ◽

Vol 745 ◽

pp. 126-136 ◽

Cited By ~ 14

Author(s):

B.B. Wu ◽

X.L. Wang ◽

Z.Q. Wang ◽

J.X. Zhao ◽

Y.H. Jin ◽

...

Keyword(s):

Mechanical Properties ◽

Grain Size ◽

Alloy Steel ◽

Prior Austenite ◽

High Strength ◽

Low Alloy Steel ◽

Austenite Grain Size ◽

Austenite Grain ◽

Prior Austenite Grain Size ◽

Prior Austenite Grain

Download Full-text

Tempering of Direct Quenched Low-Alloy Ultra-High-Strength Steel, Part I – Microstructure

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.922.316 ◽

2014 ◽

Vol 922 ◽

pp. 316-321 ◽

Cited By ~ 11

Author(s):

Antti J. Kaijalainen ◽

Sakari Pallaspuro ◽

David A. Porter

Keyword(s):

Grain Size ◽

Low Carbon Steel ◽

High Strength ◽

Steel Part ◽

Grain Structure ◽

Low Carbon ◽

Austenite Grain Size ◽

Direct Quenching ◽

Austenite Grain ◽

Effective Grain Size

The direct quenching of low-carbon steel has been shown to be an effective way of producing ultra-high-strength, tough structural steels in the as-quenched state without tempering. However, in the present study, the influence of tempering at 500 °C has been studied in order to evaluate the possibilities of widening the range of strengths that can be produced from a single base composition. The chosen composition was 0.1C-0.2Si-1.1Mn-0.15Mo-0.03Ti-0.002B. In order to compare direct quenching with conventional quenching, two pre-quench austenite states were studied: a thermomechanically rolled, non-recrystallized, pancaked austenite grain structure and a recrystallized, equiaxed grain structure. Quenched and quenched-and-tempered microstructures were studied using FESEM and FESEM-EBSD. The as-quenched microstructures of the reheated and quenched and direct quenched specimens were fully martensitic and martensitic-bainitic, respectively. In both cases, tempering made the needle-shaped auto-tempered carbides of the as-quenched materials more spherical. In the case of the direct quenched (DQ) material, tempering led to a notable increase in the size of the grain boundary carbides. Prior austenite grain size and effective grain size after quenching were larger in the case of reheated and quenched material (RQ). Tempering had no effect on effective grain size. The crystallographic texture of the DQ material showed strong {112}<131> and {554}<225> components. The RQ material also contained the same components, but it also contained an intense {110}<110> and {011}<100> components. The effects of these microstructural changes on tensile, impact toughness and fracture toughness are described in part II.

Download Full-text

Control of Weld HAZ Properties in Modern High Strength Pipeline Steels

Volume 3: Materials and Joining; Risk and Reliability ◽

10.1115/ipc2014-33109 ◽

2014 ◽

Cited By ~ 3

Author(s):

Frank Barbaro ◽

Lenka Kuzmikova ◽

Zhixiong Zhu ◽

Huijun Li

Keyword(s):

Fracture Toughness ◽

Grain Size ◽

Weld Zone ◽

High Strength ◽

Alloy Design ◽

Alternative Methods ◽

Coarse Grained ◽

Precipitate Size ◽

Austenite Grain Size ◽

Austenite Grain

Critical performance of modern high strength linepipe is related to the ability of the steel to maintain mechanical properties in the weld heat affected zone (HAZ). The region most susceptible to mechanical property degradation is the coarse grained HAZ, however in multipass welds, the intercritically reheated CGHAZ (ICCGHAZ) also presents challenges to maintain toughness. Currently Ti is employed to minimise austenite grain coarsening through the grain boundary pinning action of TiN precipitates. This is effective because of the high thermal stability of TiN but control of the precipitate size distribution is very much dependent on alloy design and processing conditions to ensure final weld HAZ properties, particularly toughness. This can be difficult to maintain and alternative methods are required to further improve performance of the weldments. It is now evident that increased additions of Nb in modern high temperature processed (HTP) steels have demonstrated increased control of HAZ microstructures with improved fracture toughness [1, 2]. The present paper details the microstructure - property relationship of two pipe steel grades with different alloy designs. Evaluation of the critical CGHAZ was achieved by simulation techniques, calibrated using real weld thermal cycles, to determine the influence of alloy design and specifically level of Nb on weld zone properties. The results reveal that the fracture toughness of the simulated CGHAZ in the HTP steel is superior to that of a conventional microalloyed pipeline steel grade. Toughness was related to the distribution of martensite-austenite (M-A) constituent and the effective grain size which appeared to correspond to prior austenite grain size as evidenced by examination of cleavage facet size (CFS) on fractured Charpy specimens.

Download Full-text

Study on Recrystallization Behavior of High Strength Automobile Steel Sheets Produced by CSP

Materials Science Forum ◽

10.4028/www.scientific.net/msf.475-479.153 ◽

2005 ◽

Vol 475-479 ◽

pp. 153-156

Author(s):

Zheng Zhi Zhao ◽

Yong Lin Kang ◽

Xin Ping Mao ◽

Yin Li Chen ◽

Gui Jiang Chen ◽

...

Keyword(s):

Grain Size ◽

Deformation Temperature ◽

High Strength ◽

Controlled Rolling ◽

Recrystallization Behavior ◽

Controlled Cooling ◽

Austenite Grain Size ◽

Steel Sheets ◽

Austenite Grain ◽

Automobile Steel

The recrystallization behavior of high strength automobile steel sheets (ZJ590L) developed by CSP technology is studied in this paper. The effect of the deformation temperature, reduction on the austenite grain size and the recrystallized fraction of ZJ590L steel during hot deformation has been investigated. Technique of test and analysis includes preparing stepped test piece and quantitative metallograph. The mechanism of austenite microstructure refinement has been discussed, which provides valuable references to set parameters of controlled rolling and controlled cooling process. The analysis shows that the austenite grain size fines with the increase of deformation temperature and reduction, and the recrystallized fraction increases. When the deformation temperature is above 1000°C and reduction exceeds 40%, complete recrystallization can be obtained.

Download Full-text